We're running two Exchange 2013 servers within our environment, one that's in use (live) and one that's being set up. Both servers are currently running older CU versions and I'd like to test the upgrade to the latest CU on the server that's being set up (to then upgrade the live system at a later date).

I'm concerned though that to upgrade to the latest CU requires changes to the AD Schema and it's not clear what (if any) affect this will have on the operation of the older CU server.

Can anyone supply any advise on running older CU versions of Exchange but with an upgraded AD Schema?